My 92 300CE is driving me nuts, most times it starts fine, but has high idle, 1200 rpm and then other times its hard starting and and won't stay running, when its doing the hard starting thing it almost sounds like its out of time as it stops cranking like its locking up and then starts cranking again, walk away from it for awhile and then it starts fine and will run fine for days and then for no reason it starts acting up again, anybody know what's going on?? Thanks Wayne